JP2015051417A - Sludge treatment system and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sludge treatment system and method which can reduce the amount of auxiliary fuel used in the whole system, enable miniaturization of equipment, and can reduce the exhaust amount of CO.SOLUTION: A sludge treatment system includes: a digestion tank 1 into which sludge having a total solids (TS) concentration of 4-12 wt.% is introduced and which anaerobically digests the sludge to generate digested sludge and digestion gas containing methane gas; a dehydrator 3 which dehydrates the digested sludge to obtain a dehydrated cake; a dryer 4 which dries the dehydrated cake to obtain dried sludge; a heating device 2 which heats the digestion tank 1 using the digestion gas; a heat supply device 5 which supplies heat to the dryer 4 using the digestion gas; and digestion gas supply lines GL1-GL3 which can supply the digestion gas generated in the digestion tank 1 to the heating device 2 and the heat supply device 5. The amount per day of heat which can be produced by the digestion gas generated from the digestion tank 1 is larger than the sum of the necessary amount per day of heat required for heating the digestion tank 1 and the necessary amount per day of heat required for drying the dehydrated cake by the dryer 4.

Description

  The present invention relates to a sludge treatment system and a sludge treatment method.

  A technology is known in which sludge generated in a wastewater treatment facility is fermented to generate digestion gas containing methane gas, and the digestion gas is effectively used as a fuel for a generator. For example, in Japanese Patent Laid-Open No. 2002-310419 (Patent Document 1), electric power is obtained by introducing digestion gas containing methane gas from organic fermentation into a combustor of a power generation facility, and is added to a reheating furnace for a pyrolysis furnace. The technology which supplements the heat source of a pyrolysis furnace by burning is disclosed.

  Japanese Patent Application Laid-Open No. 2004-66094 (Patent Document 2) discloses a technique of using digestion gas obtained by methane fermentation for power generation and using exhaust heat generated by gas power generation as a heat source of a dryer. . Japanese Patent Application Laid-Open No. 2007-260538 (Patent Document 3) discloses a technique for producing a methane fermentation gas by subjecting a liquid organic material to a methane fermentation treatment and supplying the produced methane fermentation gas as a fuel for power generation or the like. Yes.

  Japanese Patent Application Laid-Open No. 2004-284817 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2005-319373 (Patent Document 5) disclose a technique of using digestion gas generated by methane fermentation as a fuel in carbonization.

  As a technology capable of reducing the size of the anaerobic digestion facility, International Publication No. 2012/077778 (Patent Document 6) and International Publication No. 2012/147467 (Patent Document 7) have been proposed. According to the techniques of Patent Documents 6 and 7, since a sludge concentrate having a high sludge concentration of 4 to 12 wt% can be anaerobically digested in a short time, the digester capacity can be reduced and the equipment can be downsized.

JP 2002-310419 A JP 2004-66094 A JP 2007-260538 A Japanese Patent Laid-Open No. 2004-284817 JP 2005-319373 A International Publication No. 2012/077778 International Publication No. 2012/147467

  However, there is still room for improvement in technology for effectively using digestion gas generated from sludge. For example, in the conventional methane fermentation treatment technology as described in Patent Documents 1 to 6, since a large-capacity anaerobic digestion facility is used to treat sludge, a large-capacity digestion facility is heated. Needed a lot of auxiliary fuel.

  In addition, the inventions described in Patent Documents 6 and 7 also lack specific considerations for reducing auxiliary fuel in the entire system. For example, Patent Document 7 describes in detail the technology for easily concentrating sludge to a high concentration, but there is no specific mention about the use of biogas obtained from sludge. Patent Document 6 suggests that biogas generated from an anaerobic digester can be used for gas turbines, biogas boilers, gas tanks, dryer heat sources, etc., but reduces auxiliary fuel in the system. No specific measures have been taken to do this.

In view of the above problems, the present invention provides a sludge treatment system and a sludge treatment method capable of reducing the amount of auxiliary fuel used in the entire system, reducing the size of the equipment, and reducing CO ₂ emission.

  As a result of intensive studies, the inventor has arranged a small digester capable of treating sludge concentrated at a higher concentration than sludge generally used in conventional methane fermentation in a short period of time, and is obtained from the digester. Necessary for heating the digester itself and heating the dryer by using the digestion gas obtained from the digester by providing a digestion gas supply line that supplies the heated gas to the digester heating device and dryer heat supply device It was found that a sufficient amount of heat can be covered and the use of auxiliary fuel can be reduced.

  The present invention completed on the basis of the above knowledge, in one aspect, introduces a sludge having a TS concentration of 4 to 12 wt% and anaerobically digests the sludge to generate digestion gas containing methane gas and digested sludge. A tank, a dehydrator for dewatering digested sludge to obtain a dehydrated cake, a dryer for drying dehydrated cake to obtain dry sludge, a heating device for heating the digestion tank using digestion gas, and a digestion gas A sludge treatment system comprising a heat supply device for supplying heat to a dryer and a digestion gas supply line capable of supplying digestion gas generated in the digestion tank to a heating device and a heat supply device, from the digestion tank The amount of heat per day that can be generated from the generated digestion gas is the sum of the amount of heat required per day required for heating the digester and the amount of heat required per day required for drying the dehydrated cake by the dryer. Also large It is a sludge treatment system.

  In one embodiment, the sludge treatment system according to the present invention has a hydraulic retention time of 20 days or less in the digester.

  In another embodiment, the sludge treatment system according to the present invention has a sludge decomposition rate of 50 to 60% in the digestion tank.

  In yet another embodiment of the sludge treatment system according to the present invention, the dehydrator generates a dehydrated cake having a moisture content of 70 to 83%.

  In still another embodiment of the sludge treatment system according to the present invention, the drying efficiency of the dryer is 50% or more.

  In still another embodiment, the sludge treatment system according to the present invention is a supply for supplying surplus digestion gas other than digestion gas supplied to the heating device and the heat supply device to the power generation facility by the digestion gas supply line. With line.

  In yet another embodiment, the sludge treatment system according to the present invention further includes a dry sludge charging line for charging the dried sludge into the heat supply device.

  In yet another embodiment, the sludge treatment system according to the present invention further includes an aeration tank capable of treating the exhaust gas discharged from the dryer.

  In yet another embodiment, the sludge treatment system according to the present invention is a gas holder for storing digestion gas generated in a digestion tank, calculates a required heating heat amount based on the outside air temperature, and calculates the required drying heat amount with water content of the dried sludge. The calculated digestion gas amount corresponding to the calculated required heating calorie and the required drying calorie is converted based on the rate and the drying efficiency of the dryer, respectively, and the digestion gas supply line from the gas holder is calculated based on the converted digestion gas amount And a control means for controlling the amount of digestion gas supplied to the heating device and the heat supply device respectively.

  In another aspect of the present invention, a sludge having a TS concentration of 4 to 12 wt% is introduced, and the sludge is subjected to anaerobic digestion to obtain a digestion tank containing methane gas and digested sludge, and the digested sludge is dehydrated. Dehydrator to obtain dehydrated cake, carbonization equipment to carbonize dehydrated cake to obtain carbonized sludge, heating device to heat digestion tank using digestion gas, and supply heat to carbonization equipment using digestion gas And a digestion gas supply line capable of supplying digestion gas generated in the digestion tank to the heating device and the heat supply apparatus, and can be generated by digestion gas generated from the digestion tank This is a sludge treatment system in which the amount of heat per day is greater than the sum of the amount of heat required per day required for heating the digester and the amount of heat required per day required for carbonization of the dehydrated cake by the carbonization facility. .

  In yet another embodiment of the sludge treatment system according to the present invention, the hydraulic residence time of the digester is 20 days or less.

  In yet another embodiment of the sludge treatment system according to the present invention, the dehydrator generates a dehydrated cake having a moisture content of 70 to 83%.

  In yet another embodiment of the sludge treatment system according to the present invention, the digestion gas supply line generates power for supplying surplus digestion gas other than the digestion gas supplied to the heating device and the heat supply device to the power generation facility. Provide a supply line.

  In yet another embodiment, the sludge treatment system according to the present invention further includes a carbonized sludge charging line for charging the carbonized sludge into the heat supply device.

  In yet another embodiment, the sludge treatment system according to the present invention further includes an aeration tank capable of treating the exhaust gas discharged from the carbonization facility.

  In yet another embodiment, the sludge treatment system according to the present invention is a gas holder for storing digestion gas generated in a digestion tank, calculates a required heating calorific value based on the outside air temperature, and calculates the required carbonization calorific value as water content of the dehydrated cake. The calculated digestion gas amount corresponding to the calculated required heating calorific value and the required carbonization calorie amount is calculated based on the rate, respectively, and the heating device from the gas holder through the digestion gas supply line based on the converted digestion gas amount And a control means for controlling the amount of digestion gas supplied to each of the heat supply devices.

  Still another aspect of the present invention is to introduce a sludge having a TS concentration of 4 to 12 wt% into the digestion tank and anaerobically digest the sludge, thereby generating digested gas containing methane gas and digested sludge, Dewatering digested sludge with a dehydrator to produce a dehydrated cake, drying the dehydrated cake with a dryer to produce dry sludge, and heating the digester with digestion gas with a heating device Sludge treatment including supplying heat to the dryer using digestion gas by a heat supply device, and supplying digestion gas generated in the digestion tank to the heating device and the heat supply device through the digestion gas supply line The amount of heat per day that can be generated by the digestion gas generated from the digester is required for heating the digester and the required amount of heat per day for drying the dehydrated cake by the dryer. A great sludge processing method than the sum of the daily required drying heat.

  Still another aspect of the present invention is to introduce a sludge having a TS concentration of 4 to 12 wt% into the digestion tank and anaerobically digest the sludge, thereby generating digested gas containing methane gas and digested sludge, Dewatering digested sludge with a dehydrator to produce a dehydrated cake, carbonizing the dehydrated cake with a carbonization facility to produce carbonized sludge, and heating the digester with digestion gas with a heating device Sludge treatment including supplying heat to the carbonization facility using digestion gas by a heat supply device, and supplying digestion gas generated in the digestion tank to a heating device and a heat supply device through a digestion gas supply line The amount of heat per day that can be generated by the digestion gas generated from the digester is used for the required amount of heat per day required for heating the digester and the carbonization of the dehydrated cake by the carbonization equipment. A great sludge processing method than the sum of the principal of daily required drying heat.

  In one embodiment, the sludge treatment method according to the present invention treats the sludge with a hydraulic residence time of 20 days or less.

  In another embodiment, the sludge treatment method according to the present invention includes adjusting the moisture content of the dewatered cake to 70 to 83%.

  In the present invention, “%” means “% by mass” unless otherwise specified. The sludge treatment system according to the present invention can appropriately include means for sending sludge between each unique apparatus, for example, a pipe, a pump, a valve, and the like.

According to the present invention, it is possible to obtain a sludge treatment system and a sludge treatment method capable of reducing the amount of auxiliary fuel used in the entire system, miniaturizing equipment, and reducing CO ₂ emission.

It is the schematic which shows an example of the sludge processing system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows an example of the control algorithm of the control means of FIG. The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed 70%. (Part 1). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed 70%. (Part 2). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed 70%. (Part 3). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 60%. (Part 1). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 60%. (Part 2). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 60%. (Part 3). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 50%. (Part 1). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 50%. (Part 2). The table | surface showing the relationship between the suitable supply sludge density | concentration which should be supplied to a digester, and a dehydrated cake moisture content, when the sludge treatment system which concerns on 1st Embodiment is drive | operated throughout the year and drying efficiency is assumed to be 50%. (Part 3). It is a table | surface showing the trial calculation result at the time of applying the digester tank of the conventional sludge process to the digester tank of FIG. It is the schematic showing an example of the sludge processing system concerning the 2nd Embodiment of this invention. It is a flowchart which shows an example of the control algorithm of the control means of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention specifies the structure, arrangement, etc. of components as follows. Not what you want.

(First embodiment)
<Sludge treatment system>
As shown in FIG. 1, the sludge treatment system according to the first embodiment of the present invention includes a digester tank 1 that generates digested gas containing methane gas and digested sludge by anaerobically digesting sludge, and a digester tank. Heating device 2 for heating 1, dehydrator 3 for dewatering digested sludge to obtain a dehydrated cake, dryer 4 for drying dehydrated cake to obtain dry sludge, and heat for supplying heat to dryer 4 A digestion gas supply line GL (GL1 to GL3) capable of supplying digestion gas generated in the digestion tank 1 to the heating device 2 and the heat supply device 5 is provided.

  In the present invention, “sludge” means sludge discharged in a process of treating organic substances such as sewage, manure, and soot. The sludge is preferably at least one selected from an initial sludge generated from the first sedimentation basin of the wastewater treatment facility and an excess sludge generated from the final sedimentation basin, and is further a mixed sludge from both. preferable.

  The sludge is preferably sludge stored in a storage tank and obtained by gravity concentration. It is preferable to add inorganic flocculants such as polyferric sulfate, PAC, sulfuric acid band, or organic polymer flocculants to the sludge alone or in combination. Organic waste liquid or waste carried from outside the wastewater treatment plant can be further included as sludge. The organic waste liquid or waste brought in from the outside includes at least an organic compound discharged from facilities such as factories and sewage treatment plants, and may include sludge, herbs, and the like.

  Although it does not specifically limit as the digester 1, It is preferable to use a complete mixed digester. In an anaerobic digestion tank, stirring is indispensable for homogenizing the liquid in the tank and uniforming the temperature distribution and preventing the occurrence of scum. As the stirring method, it is most effective to use a mechanical stirring method, but it is also effective to attach a pump stirring method or a gas stirring method depending on the equipment environment and processing conditions. If it is a digestion tank 1 having a watertight and airtight structure with these requirements, it may be made of either reinforced concrete or steel plate, and the existing anaerobic digester should be modified or renewed according to the processing conditions. It is also applicable.

  In the digester 1 of FIG. 1, sludge having a TS (Total Solids) concentration of 4 to 12 wt%, preferably 6 to 12 wt% is introduced. In the present general sludge anaerobic digestion technology, the supply sludge has a TS concentration of 2 to 3 wt%. In this embodiment, a sludge having a TS concentration of 4 to 12 wt% higher than the conventional one is supplied to the digester 1. By introducing, high-concentration sludge can be introduced in a small volume, and a large amount of digestion gas can be generated from the small-capacity digester 1.

  The anaerobic digestion of the sludge is performed at a treatment temperature of 30 to 60 ° C. and an HRT (hydraulic residence time) of 20 days or less, more preferably 15 days or less, and even more preferably 12 days or less. In this case, the sludge decomposition rate is 50 to 60%, more specifically 55 to 58%. The capacity of the digester 1 is generally determined by the capacity of the input raw material (sludge) and HRT. Therefore, the sludge having a TS concentration of 2 to 3 wt% is treated for about 30 days by arranging the digestion tank 1 capable of implementing the sludge having a TS concentration of 4 to 12 wt% in HRT 20 days or less as in this embodiment. Since the volume of the digestion tank 1 can be reduced to about 1/2 to 1/8 of the digestion tank for conventional sludge digestion, the installation space can be reduced and the entire system can be downsized.

  Although this invention is not restrict | limited to the following conditions, the anaerobic digestion of the sludge in the digestion tank 1 is a methane from the first-stage digestion process which solubilizes sludge and acid-fermentation, and the sludge processed by the first-stage digestion process. You may carry out by the methane fermentation process which ferments and adjusts digested sludge. The pre-stage digestion process has a function to promote the anaerobic treatment of the methane fermentation process, so that HRT in the subsequent methane fermentation process can be reduced and the recovery of digestion gas (biogas) is made efficient and stable. It is possible to maintain the high content of the crude suspended solids stably and to reduce the viscosity of the fermentation broth.

  The pre-stage digestion step can be performed, for example, under conditions of a processing temperature of 30 to 60 ° C. and an HRT of 1 to 3 days. For example, the methane fermentation step is preferably performed at a treatment temperature of 30 to 60 ° C. and an HRT of 17 days or less, more preferably about 10 to 15 days, and the content of crude suspended solids with respect to SS (suspended particles) of sludge is 3 to 20% by mass. It is preferably adjusted to 5 to 18% by mass. The coarse suspended substance means a fibrous or granular substance such as cellulose. As a result, the dewaterability of the digested sludge concentrate can be improved and the moisture content of the dewatered cake can be reduced.

  The digested sludge generated in the digester 1 is dehydrated by the dehydrator 3 to obtain a dehydrated cake. The dehydrator 3 is not particularly limited and a known device can be used. For example, the digested sludge can be dehydrated by a filter press machine, a centrifuge, a screw press machine, a belt press machine, a vacuum dehydrator or the like. In addition, the separation liquid separated from the digested sludge when the dehydrated cake is generated can be water-treated by the water treatment facility 9a.

  In general, the amount of heat required for drying in the dryer 4 can be reduced as the dehydrated cake having a lower moisture content is produced by the dehydrator 3. However, if the moisture content of the digested sludge is reduced excessively, the dehydration time becomes longer and the processing efficiency may deteriorate. In addition, when the sludge is difficult to dehydrate, the sludge moisture content may not be sufficiently lowered even if the dewatering time is extended. On the other hand, if the moisture content of the dehydrated cake is too high, the digestion gas cannot cover all the heat necessary for heating the digester 1 by the heating device 2 and supplying heat to the dryer 4 by the heat supply device 5. There is.

  Therefore, in order to effectively use the digestion gas obtained in the digestion tank 1 by the heating of the heating device 2 and the heat supply of the heat supply device 5, the moisture content of the dehydrated cake should be 83% or less. More preferably, it is 81% or less, More preferably, it is 79% or less. The lower limit of the moisture content is generally preferably as low as possible and is not limited to the following, but is typically 60% or more, more preferably 70% or more, still more preferably 75% or more, and still more preferably 78. % Or more.

  According to this system, even if the moisture content of the dehydrated cake is not adjusted so low, heating of the digester 1 and heat supply to the dryer 4 during operation of this system are performed by the amount of heat of digestion gas obtained from the digester 1. It is possible to cover almost 100% of the heat required for heating. Thereby, since the auxiliary fuel supplied to the heating device 2 and the heat supply device 5 becomes unnecessary in principle, the amount of auxiliary fuel used can be reduced.

  In the dryer 4, the dehydrated cake generated in the dehydrator 3 is heated to generate dry sludge having a water content of about 10 to 40%. The dryer 4 is not particularly limited and a known device can be used.

  Considering a mode in which the heat supply to the digester 1 and the dryer 4 is supplemented only by the digestion gas obtained by this system and the auxiliary fuel is not used as much as possible, the drying efficiency of the dryer 4 is 50% or more, more preferably 60. % Or more, more preferably 70% or more. “Drying efficiency” means the ratio of the amount of heat required for evaporation of the water contained in the actual dehydrated cake to the amount of heat supplied from the heat supply device 5 to the dryer 4.

  The dried sludge obtained by the dryer 4 is granulated into a predetermined shape and particle size by the granulator 8 and then carried out of the field. Or the dry sludge obtained with the dryer 4 can be supplied to the heat supply apparatus 5 via the dry sludge line DSL comprised by piping etc. By using the dried sludge with the heat supply device 5, the dried sludge can be made into incinerated ash, so that the amount of dried sludge carried out of the field can be reduced or eliminated compared to the case where all the dried sludge is carried out of the field. The system can be made more efficient. Further, the efficiency of the system in terms of the environment can be improved, such as increasing the amount of digestion gas that can be used for power generation and the like by using the combustion heat of the dried sludge. In the sludge treatment system according to the first embodiment, the granulator 8 is not essential and may not be particularly arranged.

  The exhaust gas generated in the dryer 4 is sent to the exhaust gas treatment facility 9b. Here, part or all of the exhaust gas generated in the dryer 4 can be sent to the water treatment facility 9a. An aeration tank (not shown) is provided in the water treatment facility 9a. By introducing the exhaust gas generated in the dryer 4 into the aeration tank provided in the water treatment facility 9a, the exhaust gas can be water-treated.

  On the other hand, the digestion gas produced | generated by digestion of the sludge of the digestion tank 1 of FIG. 1 is supplied to the primary purification equipment 11 via piping etc., and impurities, such as a sulfur content, are removed. The digestion gas purified by the primary purification equipment 11 is supplied into the gas holder 12 through piping or the like. The gas holder 12 temporarily holds the purified digestion gas supplied from the primary purification equipment 11.

  The gas holder 12 includes a digestion gas supply line GL1 that can supply digestion gas generated in the digestion tank 1 to the heating device 2, and a digestion gas supply line that can supply digestion gas generated in the digestion tank 1 to the heat supply device 5. A digestion gas supply line GL3 for supplying surplus digestion gas other than the digestion gas supplied to the GL 2 and the heating device 2 and the heat supply device 5 to the power generation facility 7 is connected.

  The heating device 2 heats the digester 1 to a certain temperature (for example, 35 ° C.) using digestion gas. The type of the heating device 2 is not particularly limited, and various devices can be used. For example, the heating device 2 may be a heat source device such as a boiler that transfers heat obtained by burning digestion gas to water and replaces it with water vapor or hot water.

  The heat supply device 5 is not particularly limited as long as it is a device that supplies heat to the dryer 4 using digestion gas. For example, the heat supply device 5 may be a hot stove for burning the digestion gas to obtain the hot air gas, or a boiler that generates steam using the digestion gas. As the power generation facility 7, a known power generation facility can be used.

  The gas holder 12 may be connected to a control means 3a for adjusting the amount of digestion gas supplied from the gas holder 12 to the digestion gas supply lines GL1 to GL3. As the control means 3a, for example, a general-purpose or dedicated computer (computer) that sends a predetermined operation command can be used based on a control algorithm according to the present invention.

  Although not shown, the control means 3a calculates an amount of heat necessary for heating the digester 1 per day (hereinafter referred to as “necessary heating heat amount”) based on the outside air temperature, and an extraction unit that extracts the measurement result of the outside air temperature. A calculation unit for calculating the amount of heat per day (hereinafter referred to as “necessary drying heat amount”) necessary for drying the dehydrated cake processed by the dryer 4 based on the moisture content of the dried sludge and the drying efficiency of the dryer; The conversion unit that converts the necessary heating heat amount and the required drying heat amount calculated by the calculation unit into the digestion gas capacity necessary for supplementing the calorific value of the digestion gas, and outputs the conversion result to the gas holder 12, and the digestion gas from the gas holder An adjustment unit that generates a signal for adjusting the amount of digestion gas to be supplied to the power generation facility 7 through the supply lines GL1, GL2, and GL3, respectively. Can

According to the sludge treatment system which concerns on 1st Embodiment, the digestion tank which introduce | transduces the sludge of 4-12 wt% of TS density | concentration, and produces | generates the digestion gas and digestion sludge containing methane gas by anaerobically digesting this sludge 1 is arranged. Since this digester 1 is a small digester capable of digesting sludge to HRT 20 days or less, more preferably 15 days or less to a decomposition rate of about 50 to 60%, a large digester used for conventional sludge treatment. As compared with the above, the amount of heat required for heating the digester 1 can be reduced. As a result, the amount of heat per day that can be generated by the digestion gas generated from the digester 1 is the amount of heat required per day required for heating the digester 1 and the amount of heat required for drying the dehydrated cake by the dryer 4. Since it becomes larger than the sum of the required amount of drying heat per day, it is possible to supplement 100% of the heat required for the digester 1 and the dryer 4 with digestion gas, and a system in which no auxiliary fuel is required in principle can be constructed. By reducing the use of auxiliary fuel, the amount of CO ₂ used in the entire system is also reduced. Moreover, the miniaturization of the whole system is also attained by arrange | positioning the small digestion tank 1 processed in HRT 20 days or less.

<Sludge treatment method>
Next, the sludge treatment method according to the first embodiment of the present invention will be described. In the sludge treatment method according to the first embodiment, first, sludge having a TS concentration of 4 to 12 wt% is introduced into the digestion tank 1. The digester 1 is heated to a treatment temperature of 30 to 60 ° C. by the heating device 2, and HRT is 20 days or less, preferably about 12 to 17 days, more preferably 15 days while stirring the sludge supplied into the digester 1. Digested sludge and digestion gas are generated by the treatment. The sludge decomposition rate at this time is about 50 to 60%. The generated digested gas is subjected to a desulfurization process or the like in the primary purification equipment 11 and stored in the gas holder 12. Digested sludge is supplied to the dehydrator 3.

  In the dehydrator 3, the digested sludge is subjected to solid-liquid separation, and a dehydrated cake and a separated liquid are generated. The moisture content is preferably adjusted to be lower in consideration of the drying efficiency of the dryer 4. However, in the dehydration process in the present system, for example, it is sufficient to adjust the moisture content of the dehydrated cake to be 70 to 83%. . The dehydrated cake obtained by the dehydrator 3 is put into the dryer 4. The separated liquid is sent to the water treatment facility 9a.

  In the dryer 4, the dehydrated cake is dried by heat such as hot air gas supplied from the heat supply device 5 to generate dry sludge having a moisture content of about 10 to 40%. The obtained dried sludge is granulated to a predetermined size and shape by the granulator 8 as necessary, and then carried out of the field. Alternatively, the obtained dried sludge can be put into the heat supply device 5. The exhaust gas generated in the dryer 4 is purified by being sent to the exhaust gas treatment facility 9b or by being supplied into the aeration tank of the water treatment facility 9a.

  The digestion gas stored in the gas holder 12 is supplied to the heating device 2, the heat supply device 5, and, if necessary, the power generation facility 7 through the digestion gas supply lines GL1 to GL3. The control means 3a calculates the amount of digestion gas to be supplied in order to control the amount of digestion gas supplied from the gas holder 12 to the heating device 2 and the heat supply device 5 via the digestion gas supply lines GL1 to GL3. Here, an example of a digestion gas amount calculation method by the control means 3a will be described using the flowchart of FIG.

  In step S11 of FIG. 2, the ambient temperature around the sludge treatment system is extracted by the extraction unit of the control means 3a. In step S <b> 12, the calculation unit of the control unit 3 a compares the set temperature of the digestion tank 1 with the outside air temperature and determines how many times the temperature of the digestion tank 1 should be increased (temperature increase temperature). The calculation unit is further required for heating the digestion tank 1 based on the volume of the sludge charged into the digestion tank 1, the temperature rise temperature of the digestion tank 1, the amount of heat released from the digestion tank 1, and the temperature rise efficiency of the digestion tank 1. Calculate the required amount of heat per day. In step S13, the calculation unit of the control means 3a is based on the weight and moisture content of the dehydrated cake put into the dryer 4, the amount of evaporated water necessary for drying, the moisture content of the dried sludge, and the drying efficiency of the dryer 4. The necessary amount of drying heat per day necessary for drying the dewatered cake in the dryer 4 is calculated. In step S <b> 14, the conversion unit of the control unit 3 a converts the volume of digestion gas having a calorific value corresponding to the required heating heat amount and the required drying heat amount calculated by the calculation unit. In step S <b> 15, the adjustment unit of the control unit 3 a outputs the conversion result to the gas holder 12. As a result, the digestion gas is distributed from the gas holder 12 to the heating device 2 and the heat supply device 5.

According to the sludge treatment method according to the first embodiment, the digestion gas generated from the digestion tank 1 is supplied to the heating apparatus 2 that heats the digestion tank 1 and the heat supply apparatus 5 that supplies heat to the dryer 4. Supplied. The digestion tank 1 of FIG. 1 is smaller than a digestion tank that treats sludge having a sludge concentration of about 2 to 3%, and therefore requires less heat for heating. As a result, all the heat required for heating the digester 1 and supplying heat to the dryer 4 can be supplemented by heat generated by digestion gas combustion or the like. Therefore, since the auxiliary fuel is not used for heating the digester 1 and the dryer 4 during the steady operation, the CO ₂ emission amount can be reduced as a whole system.

(First calculation result)
An example of a trial calculation result when raw sludge is treated by introducing the sludge treatment system shown in FIG. 1 is shown below.

1. Raw sludge to be treated Conditions of raw sludge to be treated were assumed as follows.
Annual sludge volume 503883t / year (1381m ³ / day)
Sludge moisture content 99%
TS 10000mg / L (13.81tTS / day)
VS 8000mg / L (11.04tVS / day)
Methane gas generation rate 550L / kgΔVS
Methane gas calorific value 35.8 MJ / m ³ N-CH ₄

2. Supply sludge to be supplied to digester 1 Raw sludge was concentrated to increase the concentration and reduce the volume to obtain supply sludge.
TS 80000mg / L (13.81tTS / day)
VS 64000mg / L (11.04tVS / day)
Supply sludge organic fraction (VS / TS) 0.8
Supply sludge TS concentration 8%
Supply sludge capacity: 173m ³ / day

3. Digestion Supply sludge with high concentration and low capacity is supplied to the digestion tank 1 of FIG. 1, the digestion tank 1 is heated to 35 ° C. using the heating device 2, and the decomposition rate is 15 days (HRT). Assuming that the anaerobic treatment of sludge at 58% was carried out, the digester capacity was determined.
Digestion tank capacity = input raw material capacity × HRT = 173 × 15 = about 2600 m ³

4). Trial Calculation Results of Digested Sludge and Digested Gas Digested sludge, digested gas amount obtained from digesting sludge in digestion tank 1 having the above capacity, digested gas amount, and calorific value (calorific value) obtained per day were calculated.
<Digested sludge>
Digested sludge capacity approx. 173m ³ / day
Digested sludge TS = (Supply sludge TS-Supply sludge VS x Decomposition rate)
= 13.81-11.04 × 0.58 = about 7.4 tTS / day <digestion gas>
Hydrogen sulfide content 2000ppm or less Methane gas generation amount = (Supply sludge VS x Decomposition rate x Methane gas generation rate)
= About 3523 m ³ / day Digestion gas generation capacity assuming a methane gas content of 60% = About 5872 m ³ / day Lower heating value = Methane gas heating value × Methane gas fraction = 21480 kJ / m ³
The amount of heat (calorific value) obtained from digestion gas per day =
Lower heating value x digestion gas generation capacity = approx. 126125 MJ / day

5. Assuming that the water content of the dehydrated cake obtained by the dehydrator 3 and the recovery rate of the dehydrated cake from the dehydrator 3 were as follows, it was estimated that the following dehydrated cake was obtained.
Water content of dehydrated cake 77%
Dehydration cake recovery rate 95%
Recovered dehydrated cake TS = digested sludge TS × recovery rate = about 7.0 tTS / day Recovered dehydrated cake weight = digested sludge TS / (1-water content) = about 31 t / day

6). Drying The weight of the dried sludge was calculated assuming that the moisture content of the dried sludge obtained from the dewatered cake taken out from the dehydrator 3 was 20%.
Dry sludge weight obtained per day = dehydrated cake TS / (1-water content)
= About 8.8t / day

7). Heating amount required for the heating device 2 The amount of heat per day (necessary heating amount) required for heating the digester 1 of the heating device 2 was estimated.
Digestion tank 1 temperature rise 20 ° C (assuming digestion sludge temperature 15 ° C)
Heat dissipation 0.30 ° C / m ³ days Heating efficiency 80%
Necessary heating heat amount = (Supply sludge capacity x Temperature rise temperature + Digestion tank 1 capacity x Heat release amount) / Heating efficiency
= Approx. 22140 MJ / day

8). Equivalent digestion gas volume (capacity) to be used for heating the digester 1
Equivalent digestion gas amount for temperature rise = Necessary heating calorie / Digestion gas lower calorific value = About 1031 m ³ / day

9. Required amount of drying heat of the heat supply device 5 The amount of heat necessary for the heat supply of the dryer 4 by the heat supply device 5 per day (necessary drying heat amount) was calculated.
Dehydrated cake temperature Increased from 20 ℃ to 100 ℃ Latent heat 2.258kJ / kg
Sensible heat 4.186kJ / kg ・ ℃
70% drying efficiency
Evaporated moisture = recovered dehydrated cake-dried sludge = 22 t / day Necessary drying heat = {evaporated moisture x latent heat + (moisture in dehydrated cake) x (change in temperature of dehydrated cake) x sensible heat} / drying efficiency = about 81502 MJ / Day

10. Equivalent digestion gas volume (capacity) to be used for the heat supply device 5
Equivalent digestion gas amount for heat supply = heat amount of heat supply device / lower heating value
= About 3794m ³ / day

11. Surplus gas (Amount of gas that can be supplied to power generation facilities, etc.)
The surplus gas after supplying the digestion gas obtained in the digester 1 to the heating device 2 and the heat supply device 5 was estimated.
Surplus gas = digestion gas generation capacity-equivalent amount of gas to be used for heating the digester 1-equivalent amount of digestion gas to be used for the heat supply device 5
= Approximately 1047m ³ / day

  According to the above calculation results, the amount of heat per day that can be generated by the digestion gas generated from the digester 1 is the required amount of heat per day required for heating the digester 1 and the drying of the dehydrated cake by the dryer. It becomes larger than the sum of the required amount of dry heat per day necessary for the above. That is, it can be seen that the digestion gas generated from the digestion tank 1 can supplement all the heat necessary for heating the digestion tank 1 and drying the dehydrated cake by the dryer 4.

12 Annual income and expenditure Based on the average monthly temperature, the digestion gas generated in the digester 1 was used to calculate whether the heat required for heating the digester 1 and drying the dryer 4 could be compensated throughout the year. . Here, calculations were made using average monthly temperature data in Gamagori City, Aichi Prefecture. The sludge temperature in the digester 1 was assumed to be 15 ° C. when the outside temperature was less than 15 ° C., the outside temperature was assumed to be 35 ° C. when the outside temperature was 15 ° C. or higher, and the digester set temperature was assumed to be 35 ° C. The amount of heat released from the digester 1 is 0.3 ° C / m ³ days when the temperature difference is 20 ° C, and the temperature rises every month based on the relationship between the sludge temperature and the digester set temperature (35 ° C). Temperature and heat dissipation were calculated respectively. Based on the obtained monthly temperature rise and heat release, the required heating heat and required drying heat required for heating the digester 1 were calculated for each month. The obtained required heating heat amount and required drying heat amount were subtracted from the heating value of the digestion gas obtained from the digestion tank 1, and the surplus gas amount was estimated. Table 1 shows the results of the trial calculation.

As shown in Table 1, sludge having a TS concentration of about 8% is operated on a digestion tank 1 having a capacity of about 2600 m ³ on HRT 15 days (decomposition rate 58%), the moisture content of the dehydrated cake is 77%, and the drying efficiency is 70%. When operating at%, even if the digestion gas generated from the digestion tank 1 is used for heating the digestion tank 1 and supplying heat to the dryer 4, it can be seen that surplus gas is generated throughout the year. According to the first embodiment, the digestion gas generated from the digester 1 can make up for 100% of the amount of heat necessary for heating the digester 1 and supplying heat to the dryer 4. The system can be made more efficient by using less auxiliary fuel.

(Second estimation result)
In the sludge treatment system shown in FIG. 1, the concentration of sludge supplied to the digester 1, the number of days of sludge treatment (HRT), the sludge decomposition rate, the organic fraction of the supplied sludge, the dewatering rate of the dehydrated cake, and the drying efficiency of the dryer are shown. About the case where it changed, it was estimated whether the heat | fever required for the heating to the digester 1 and the heat supply to the dryer 4 could be compensated 100% with the digestion gas generated from the digester 1 throughout the year. The trial calculation results are shown in FIGS. In addition, in FIGS. 3-11, the case where all the heat | fever required for the heating of the digestion tank 1 and the heat supply to the dryer 4 can be supplemented with the heat | fever which can be produced | generated with digestion gas throughout the year is "(circle)", and a part The case where only the month is compensated is represented by “Δ”, and the case where it is not supplemented is represented by “x”.

(Third trial calculation result)
The amount of raw sludge to be treated is the same as the result of the first calculation, and the supply sludge supplied to the digester 1 is concentrated to 3% (supply sludge capacity: 460 m ³ / day), which is a general supply concentration. Except for the case where the sludge was anaerobically digested on the 30th day of HRT, the heat balance was calculated using the same procedure and conditions as the first trial calculation result. As a result, the capacity of the digester 1 was increased to 13900 m ³ and the system was enlarged. . Furthermore, as a result of the trial calculation of the heat balance of the entire system in the same procedure as the first trial calculation result, only the digestion gas generated from the digestion tank 1 has the amount of heat necessary for heating the digestion tank 1 and supplying heat to the dryer 4. 100% could not be compensated.

  Furthermore, when the sludge decomposition efficiency, dehydrated cake water content, sludge organic content, and drying efficiency of the dryer 4 were changed, the annual balance was calculated in the same procedure as the second calculation result. The results are shown in FIG. In the third calculation result, the capacity of the digester is significantly larger than that of the digester 1 according to the first embodiment, and the water content of the dehydrated cake is reduced in order to reduce the amount of auxiliary fuel used in the entire system. In general, it was necessary to reduce the amount to 70% or less, and in some cases, about 60 to 65%, which resulted in a higher load on the dehydrator compared to the second calculation result.

(Second Embodiment)
<Sludge treatment system>
As shown in FIG. 13, in the sludge treatment system according to the second embodiment, instead of the dryer 4 that dries the dewatered cake, a carbonization facility 6 that carbonizes the dehydrated cake to obtain carbonized sludge is disposed. The point differs from the sludge treatment system shown in FIG. Furthermore, the control means 3b is different from the control means 3a shown in FIG. 1 in that the required amount of heat of carbonization per day necessary for carbonization of the dewatered cake by the carbonization equipment 6 is calculated. Since others are substantially the same as the sludge system shown in FIG. 1, the repeated description is abbreviate | omitted. The carbonization facility 6 is not particularly limited, and a known device can be used.

  Carbonized sludge obtained in the carbonization facility 6 is carried out of the field. Alternatively, the carbonized sludge obtained in the carbonization facility 6 can be supplied to the heat supply device 5 via the carbonized sludge line CSL constituted by piping or the like. By using the carbonized sludge in the heat supply device 5, the carbonized sludge can be made into incineration ash, so the amount of carbonized sludge carried out of the field can be reduced or eliminated compared to the case where all the carbonized sludge is carried out of the field. The system can be made more efficient. Further, the efficiency of the system in terms of the environment can be improved, such as increasing the amount of digestion gas that can be used for power generation and the like by using the combustion heat of carbonized sludge.

  The exhaust gas generated in the carbonization facility 6 is sent to the exhaust gas treatment facility 9b. Here, part or all of the exhaust gas generated in the carbonization facility 6 can be sent to the water treatment facility 9a. An aeration tank (not shown) is provided in the water treatment facility 9a. By introducing the exhaust gas generated in the carbonization facility 6 into the aeration tank provided in the water treatment facility 9a, the exhaust gas can be treated with water.

  Although not shown, the control means 3b calculates an amount of heat necessary for heating the digestion tank 1 per day (hereinafter referred to as “necessary heating heat amount”) based on the outside air temperature, and extracts an outside temperature measurement result. And a calculation unit for calculating the amount of heat per day necessary for carbonization of the dewatered cake processed by the carbonization facility 6 (hereinafter referred to as “necessary heat of carbonization”) based on the moisture content and weight of the dehydrated cake; Converts the required heating calorific value and the required carbonization calorific value into the digestion gas capacity required to supplement the calorific value of the digestion gas, and outputs the conversion result to the gas holder 12 from the gas holder to the digestion gas supply line GL1. , GL2, and GL3, the heating device 2, the heat supply device 5, and an adjustment unit that generates a signal for adjusting the amount of digestion gas that supplies surplus gas to the power generation facility 7.

According to the sludge treatment system according to the second embodiment, the amount of heat per day that can be generated by the digestion gas generated from the digester 1 is the required amount of heat per day that is necessary for heating the digester 1. Since it becomes larger than the sum of the required amount of heat of carbonization per day required for carbonization of the dewatered cake by the carbonization facility 6, it becomes possible to supplement the heat required for the digester 1 and the carbonization facility 6 by digestion gas 100%, and auxiliary fuel However, in principle, an unnecessary system can be constructed. By reducing the use of auxiliary fuel, the amount of CO ₂ used in the entire system is also reduced. Moreover, the miniaturization of the whole system is also attained by arrange | positioning the small digestion tank 1 processed in HRT 20 days or less.

<Sludge treatment method>
Next, a sludge treatment method according to the second embodiment of the present invention will be described. In the sludge treatment method according to the second embodiment, first, sludge having a TS concentration of 4 to 12 wt% is introduced into the digestion tank 1. The digester 1 is heated to a treatment temperature of 30 to 60 ° C. by the heating device 2, and HRT is 20 days or less, preferably about 12 to 17 days, more preferably 15 days while stirring the sludge supplied into the digester 1. Digested sludge and digestion gas are generated by the treatment. The sludge decomposition rate at this time is about 50 to 60%. The generated digested gas is subjected to a desulfurization process or the like in the primary purification equipment 11 and stored in the gas holder 12. Digested sludge is supplied to the dehydrator 3.

  In the dehydrator 3, the digested sludge is subjected to solid-liquid separation, and a dehydrated cake and a separated liquid are generated. The water content is preferably adjusted to be lower in consideration of the carbonization efficiency of the carbonization facility 6. However, in the dehydration process in this system, for example, it is sufficient to adjust the water content of the dehydrated cake to 70 to 83%, for example. . The dehydrated cake obtained by the dehydrator 3 is put into the carbonization facility 6.

  In the carbonization facility 6, the dehydrated cake is carbonized using heat such as hot air supplied from the heat supply device 5 to generate carbonized sludge. The obtained carbonized sludge is transported off-site. Or the obtained carbonized sludge can be thrown into the heat supply apparatus 5 via the carbonized sludge supply line CSL. The exhaust gas generated in the carbonization facility 6 is sent to an aeration tank provided in the exhaust gas treatment facility 9b and / or the water treatment facility 9a.

  The digestion gas stored in the gas holder 12 is supplied to the heating device 2, the heat supply device 5, and, if necessary, the power generation facility 7 through the digestion gas supply lines GL1 to GL3. The control means 3b calculates the amount of digestion gas to be supplied in order to control the amount of digestion gas supplied from the gas holder 12 to the heating device 2 and the heat supply device 5 via the digestion gas supply lines GL1 to GL3. Here, an example of a calculation method by the control means 3b will be described using the flowchart of FIG.

  In step S21 of FIG. 14, the ambient temperature around the sludge treatment system is extracted by the extraction unit of the control means 3b. In step S22, the calculation unit of the control unit 3b compares the set temperature of the digester 1 and the outside air temperature to determine how many times the temperature of the digester 1 should be increased (temperature increase temperature). The calculation unit is further required for heating the digestion tank 1 based on the volume of the sludge charged into the digestion tank 1, the temperature rise temperature of the digestion tank 1, the amount of heat released from the digestion tank 1, and the temperature rise efficiency of the digestion tank 1. Calculate the required amount of heat per day. In step S23, the calculation part of the control means 3b calculates the required amount of carbonization heat per day necessary for drying the dehydrated cake in the carbonization facility 6 based on the weight and moisture content of the dehydrated cake charged into the carbonization facility 6. . In step S24, the conversion unit of the control means 3b converts the volume of digestion gas having a calorific value corresponding to the required heating heat amount and the required carbonization heat amount calculated by the calculation unit. In step S <b> 25, the adjustment unit of the control unit 3 b outputs the conversion result to the gas holder 12, and the digestion gas is distributed from the gas holder 12.

According to the sludge treatment method according to the second embodiment, the digestion gas generated from the digestion tank 1 is supplied to the heating apparatus 2 that heats the digestion tank 1 and the heat supply apparatus 5 that supplies heat to the carbonization facility 6. Supplied. The digestion tank 1 of FIG. 1 is smaller than a digestion tank that treats sludge having a sludge concentration of about 2 to 3%, and therefore requires less heat for heating. Thereby, all the heat required for the heating of the digestion tank 1 and the heat supply of the carbonization facility 6 can be supplemented by the heat generated by the digestion gas combustion or the like. As a result, since auxiliary fuel is not used for heating the digester 1 and the carbonization facility 6 during steady operation, the entire system can reduce CO ₂ emissions.

(Fourth calculation result)
An example of a trial calculation result according to the second embodiment when raw sludge is treated by introducing the sludge treatment system shown in FIG. 13 is shown below.
1. Raw sludge to be treated The raw sludge to be treated was assumed as follows.
Annual sludge volume 503883t / year (1381m ³ / day)
Sludge moisture content 99%
TS 10000mg / L (13.81tTS / day)
VS 8000mg / L (11.04tVS / day)
Methane gas generation rate 550L / kgΔVS
Methane gas calorific value 35.8 MJ / m ³ N-CH ₄

2. The feed sludge raw sludge supplied to the digester 1 was concentrated to increase the concentration and reduce the volume to obtain the feed sludge.
TS 80000mg / L (13.81tTS / day)
VS 64000mg / L (11.04tVS / day)
Supply sludge organic fraction (VS / TS) 0.8
Supply sludge TS concentration 8%
Supply sludge capacity: 173m ³ / day

3. Digestion The above-mentioned supply sludge having a high concentration and a low volume is supplied to the digestion tank 1 of FIG. 13, the digestion tank 1 is heated to 35 ° C. using the heating device 2, and the treatment days (HRT) is 15 days. The digester capacity was determined on the assumption that anaerobic treatment of sludge at a rate of 58% was carried out.
Digestion tank capacity = input raw material capacity × HRT = 173 × 15 = about 2600 m ³

4). Results of Trial Calculation of Digested Sludge and Digested Gas The digested sludge obtained as a result of anaerobic digestion of the sludge in the digestion tank with the above capacity, the amount of digested gas and the amount of heat (calorific value) obtained from the digested gas per day were calculated.
<Digested sludge>
Digested sludge capacity 173m ³ / day
Digested sludge TS = (Supply sludge TS-Supply sludge VS x Decomposition rate)
= 13.81-11.04 × 0.58 = about 7.4 tTS / day <digestion gas>
Hydrogen sulfide content 2000ppm or less Methane gas generation amount = (Supply sludge VS x Decomposition rate x Methane gas generation rate)
= About 3523 m ³ / day Digestion gas generation amount assuming about 60% methane gas content = about 5872 m ³ / day Lower heating value = Methane gas heating value × Methane gas fraction = 21480 kJ / m ³
The amount of heat (calorific value) obtained from digestion gas per day =
Low calorific value x digestion gas generation amount = about 126125 MJ / day

5. Assuming that the water content of the dehydrated cake obtained by the dehydrator 3 and the recovery rate of the dehydrated cake from the dehydrator 3 were as follows, it was estimated that the following dehydrated cake was obtained.
Moisture content of dehydrated cake 82%
Dehydration cake recovery rate 95%
Collected dewatered cake TS = digested sludge TS × recovery rate = about 7.0 tTS / day Collected dewatered cake weight = digested sludge TS / (1-water content) = about 39 t / day

6). Carbonization The weight of the carbonized sludge obtained from the carbonization facility 6 per day was assumed to be TS of the dewatered cake.
Carbonized sludge weight about 7.0t / day

7). Heating amount required for the heating device 2 The amount of heat required for heating the digester 1 by the heating device 2 per day was estimated.
Digestion tank 1 temperature rise 20 ° C (assuming digestion sludge temperature 15 ° C)
Heat dissipation 0.30 ° C / m ³ days Heating efficiency 80%
Necessary heating heat amount = (Supply sludge capacity x Temperature rise temperature + Digestion tank 1 capacity x Heat release amount) / Heating efficiency
= Approx. 22108 MJ / day

8). Equivalent digestion gas amount to be used for raising the temperature of digester 1 Equivalent digestion gas amount for raising temperature = necessary heating calorie / digestion gas lower calorific value = approximately 1029 m ³ / day

9. Amount of heat of carbonization required for heat supply device 5 The amount of heat necessary for carbonization of dehydrated cake by carbonization facility 6 (the amount of heat of carbonization) per day, A heavy oil when carbonized dehydrated cake with a predetermined moisture content using A heavy oil The calculation was based on the empirical data on the relationship between the amount used and the amount of dried sludge solids. This demonstration data uses the results of trial calculations by a carbonization equipment manufacturer. Table 2 shows the relationship between the moisture content of the dehydrated cake, the amount of heavy oil A used, and the solid content of the carbonized sludge when a carbonization facility with a processing capacity of 80 t / day is used (assuming that the loss on ignition is 85%).

  From Table 2, the estimated amount of dehydrated cake at each moisture content when the solid content was 13.8 t-TS / day was estimated, and the fuel consumption and the required carbonization heat amount for each moisture content were calculated by proportional calculation with respect to 80 t / day. A heavy oil calorie low calorific value was set to 36.5 MJ / L. The results are shown in Table 3.

  From the trial calculation results in Table 3, the amount of heat necessary for carbonization of a dehydrated cake having a moisture content of 82% (necessary amount of carbonization) per day was calculated to be 92345 MJ / day.

10. Equivalent digestion gas volume (capacity) to be used for the heat supply device 5
Equivalent digestion gas for heat supply = Necessary calorific value / Lower calorific value
= Approximately 4306m ³ / day

11. Surplus gas (Amount of gas that can be supplied to power generation facilities, etc.)
The surplus gas after supplying the digestion gas obtained in the digester 1 to the heating device 2 and the heat supply device 5 was estimated.
Surplus gas = digested gas generation amount−converted gas amount to be used for heating the digester 1 −converted digestive gas amount to be used for the heat supply device 5
= Approximately 539m ³ / day

  According to the above calculation results, the amount of heat per day that can be generated by the digestion gas generated from the digester 1 is the required amount of heat per day necessary for heating the digester 1 and the dehydrated cake of the carbonization facility 6. It is larger than the sum of the required heat of carbonization per day necessary for drying. That is, the digestion gas generated from the digester 1 can compensate for all the heat necessary for heating the digester 1 and carbonizing the dehydrated cake by the carbonization facility 6.

12 Annual balance Based on the average temperature of each month, the digestion gas generated in the digester 1 was used to calculate whether the heat required for heating the digester 1 and the carbonization of the carbonization facility 6 could be compensated throughout the year. . As in the first embodiment, trial calculation was performed using average monthly temperature data in Gamagori City, Aichi Prefecture. Here, the sludge temperature in the digester 1 is assumed to be 15 ° C. when the outside air temperature is less than 15 ° C., the outside air temperature is assumed to be 35 ° C. when the outside air temperature is 15 ° C. or higher, and the digester set temperature is assumed to be 35 ° C. The amount of heat released from the digester 1 is 0.3 ° C / m ³ days when the temperature difference is 20 ° C, and the temperature rises every month based on the relationship between the sludge temperature and the digester set temperature (35 ° C). Temperature and heat dissipation were set respectively. Based on the obtained monthly temperature rise and heat release, the required heating heat and required carbonization required for heating the digester 1 were calculated for each month. The obtained required heating calorific value and required calorific value were subtracted from the calorific value of the digestion gas obtained from the digestion tank 1, and the surplus gas amount was estimated. Surplus gas was calculated. Table 4 shows the results of the trial calculation.

As shown in Table 4, when the sludge having a TS concentration of about 8% was operated on the HRT for 15 days (decomposition rate 58%) using the digester 1 having a capacity of about 2600 m ³ , and the moisture content of the dehydrated cake was 82%, Even if digestion gas generated from the digestion tank 1 is used for heating the digestion tank 1 and supplying heat to the carbonization facility 6, it can be seen that surplus gas is generated throughout the year. According to the second embodiment, the digestion gas generated from the digestion tank 1 can make up for 100% of the amount of heat necessary for heating the digestion tank 1 and heat supply for carbonization of the carbonization facility 6, It can be seen that the efficiency of the system can be improved by using less auxiliary fuel in the system.

(Other embodiments)
Although the present invention has been described according to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments and operational techniques will be apparent to those skilled in the art.

  In the sludge treatment system shown in FIG. 1 and FIG. 13, using the control means 3 a and 3 b, the necessary heating heat amount per day necessary for heating the digester 1 and the dehydrated cake by the dryer 4 or the carbonization equipment 6. Is a method for automatically calculating the required amount of heat of drying or the amount of heat of carbonization necessary for the drying or carbonization. However, the configuration for automatically calculating each heat quantity by the control means 3a, 3b is not particularly arranged, and for example, the operator can manually set each condition in the system based on only the temperature condition of the digester 1 and operate. Is possible.

  As described above, the present invention is expressed by the invention specifying matters in the scope of claims appropriate from the above disclosure, and can be modified and embodied without departing from the spirit of the invention in the implementation stage.

DESCRIPTION OF SYMBOLS 1 ... Digestion tank 2 ... Heating device 3 ... Dehydrator 3a, 3b ... Control means 4 ... Dryer 5 ... Heat supply device 6 ... Carbonization equipment 7 ... Power generation equipment 8 ... Granulator 9a ... Water treatment equipment 9b ... Exhaust gas treatment Equipment 11 ... Primary refining equipment 12 ... Gas holders GL1-GL3 ... Digestion gas supply line

Claims (20)

Introducing sludge having a TS concentration of 4 to 12 wt% and anaerobic digestion of the sludge, thereby generating digestion gas containing methane gas and digested sludge,
A dehydrator to dehydrate the digested sludge to obtain a dehydrated cake;
A dryer for drying the dehydrated cake to obtain dried sludge;
A heating device for heating the digestion tank using the digestion gas;
A heat supply device for supplying heat to the dryer using the digestion gas;
A digestion gas supply line capable of supplying digestion gas generated in the digestion tank to the heating device and the heat supply device, and a sludge treatment system comprising:
The amount of heat per day that can be generated by the digestion gas generated from the digester is the required amount of heat per day necessary for heating the digester and the amount of heat required for drying the dehydrated cake by the dryer. A sludge treatment system characterized in that it is greater than the sum of the required amount of drying heat.   The sludge treatment system according to claim 1, wherein a hydraulic residence time in the digestion tank is 20 days or less.   The sludge treatment system according to claim 1 or 2, wherein a decomposition rate of the sludge in the digestion tank is 50 to 60%.   The sludge treatment system according to any one of claims 1 to 3, wherein the dehydrator includes generating a dehydrated cake having a moisture content of 70 to 83%.   The sludge treatment system according to any one of claims 1 to 4, wherein the drying efficiency of the dryer is 50% or more.   The said digestion gas supply line is provided with the supply line for supplying surplus digestion gas other than the digestion gas supplied to the said heating apparatus and the said heat supply apparatus to an electric power generation installation. 2. The sludge treatment system according to item 1.   The sludge treatment system according to any one of claims 1 to 6, further comprising a dry sludge charging line for charging the dried sludge into the heat supply device.   The sludge treatment system according to any one of claims 1 to 7, further comprising an aeration tank capable of treating the exhaust gas discharged from the dryer. A gas holder for storing the digestion gas generated in the digestion tank;
The required heating heat amount is calculated based on the outside air temperature, the required drying heat amount is calculated based on the moisture content of the dried sludge and the drying efficiency of the dryer, and the calculated required heating heat amount and the required drying amount are calculated. The converted digestion gas amount corresponding to the amount of heat is converted respectively, and based on the converted digestion gas amount, the digestion gas amount supplied from the gas holder to the heating device and the heat supply device via the digestion gas supply line, respectively. The sludge treatment system according to any one of claims 1 to 8, further comprising control means for controlling. Introducing sludge having a TS concentration of 4 to 12 wt% and anaerobically digesting the sludge, thereby obtaining a digestion gas containing methane gas and digested sludge,
A dehydrator to dehydrate the digested sludge to obtain a dehydrated cake;
A carbonization facility for carbonizing the dehydrated cake to obtain carbonized sludge;
A heating device for heating the digestion tank using the digestion gas;
A heat supply device for supplying heat to the carbonization facility using the digestion gas;
A digestion gas supply line capable of supplying digestion gas generated in the digestion tank to the heating device and the heat supply device, and a sludge treatment system comprising:
The amount of heat per day that can be generated by the digestion gas generated from the digester is the required amount of heat per day that is necessary for heating the digester, and 1 that is necessary for the carbonization of the dehydrated cake by the carbonization facility. A sludge treatment system characterized by being larger than the sum of the required amount of carbonization per day.   The sludge treatment system according to claim 10, wherein a hydraulic residence time in the digestion tank is 20 days or less.   The sludge treatment system according to claim 10 or 11, wherein the dehydrator includes generating a dehydrated cake having a moisture content of 70 to 83%.   The said digestion gas supply line is provided with the electric power generation supply line for supplying surplus digestion gas other than the digestion gas supplied to the said heating apparatus and the said heat supply apparatus to an electric power generation installation. The sludge treatment system according to any one of the items.   The sludge treatment system according to any one of claims 10 to 13, further comprising a carbonized sludge charging line for charging the carbonized sludge into the heat supply device.   The sludge treatment system according to any one of claims 10 to 14, further comprising an aeration tank capable of treating exhaust gas discharged from the carbonization facility. A gas holder for storing digestion gas generated in the digestion tank;
The required heating heat amount is calculated based on the outside air temperature, the required carbonization heat amount is calculated based on the moisture content of the dehydrated cake, and the converted digestion gas corresponding to the calculated required heating heat amount and the required carbonization heat amount And a control means for controlling the amount of digestion gas respectively supplied to the heating device and the heat supply device from the gas holder via the digestion gas supply line based on the converted digestion gas amount. The sludge treatment system according to any one of claims 10 to 15. Introducing sludge having a TS concentration of 4 to 12 wt% into the digestion tank and anaerobically digesting the sludge to generate digested gas containing methane gas and digested sludge;
Dewatering the digested sludge with a dehydrator to produce a dehydrated cake;
Drying the dehydrated cake with a dryer to produce dry sludge;
Heating the digester using the digestion gas with a heating device;
Supplying heat to the dryer using the digestion gas by a heat supply device;
Supplying the digestion gas generated in the digestion tank to the heating device and the heat supply device through a digestion gas supply line,
The amount of heat per day that can be generated by the digestion gas generated from the digester is the required amount of heat per day necessary for heating the digester and the amount of heat required for drying the dehydrated cake by the dryer. A sludge treatment method characterized by being greater than the sum of the required amount of drying heat. Introducing sludge having a TS concentration of 4 to 12 wt% into the digestion tank and anaerobically digesting the sludge to generate digested gas containing methane gas and digested sludge;
Dewatering the digested sludge with a dehydrator to produce a dehydrated cake;
Carbonizing the dehydrated cake with a carbonization facility to produce carbonized sludge;
Heating the digester using the digestion gas with a heating device;
Supplying heat to the carbonization facility using the digestion gas by a heat supply device;
Supplying the digestion gas generated in the digestion tank to the heating device and the heat supply device through a digestion gas supply line,
The amount of heat per day that can be generated by the digestion gas generated from the digester is the required amount of heat per day required for heating the digester and the amount of heat required for carbonization of the dehydrated cake by the carbonization facility. A sludge treatment method characterized by being greater than the sum of the required amount of carbonization heat.   The sludge treatment method according to claim 17 or 18, wherein the sludge has a hydraulic residence time of 20 days or less.   The sludge treatment method according to any one of claims 17 to 19, comprising adjusting a moisture content of the dehydrated cake to 70 to 83%.

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